Room-temperature ionic liquids (RTILs) are organic salts that are liquid at or below 100° C., and are composed entirely of cations and anions (i.e., free of any additional solvents) (Welton, Chem. Rev. 1999, 99: 2071-2083; and Welton, Coord. Chem. Rev. 2004, 248:2459-2477). They have attracted broad interest as novel solvents and liquid media for a number of applications because they have a unique combination of liquid properties. They have very low volatility, relatively low viscosity, high thermal stability, low flammability, high ionic conductivity, tunable polar solvation and transport properties, and in some cases, even catalytic properties. These characteristics have made RTILs excellent candidates as environmentally benign solvents to replace conventional organic solvents in many chemical, electrochemical, and physical extraction/separation processes. In addition, RTILs have been shown to be novel gas separation media in supported liquid membranes (SLMs) and novel catalysts in a number of chemical processes, with performance enhancements in both cases due to the unique properties of RTILs (Scovazzo et al. “Supported Ionic Liquid Membranes and Facilitated Ionic Liquid Membranes,” ACS Symposium Series 818 (Ionic Liquids), 2002, 69-87; and Schaefer et al. “Opportunities for Membrane Separation Processes using Ionic Liquids,” ACS Symposium Series 902 (Ionic Liquids IIIB: Fundamentals, Progress, Challenges, and Opportunities), 2005, 97-110).
The use of RTILs on polymer supports for membrane applications has primarily been studied for catalysis and gas separations (Riisager and Fehrmann, Ionic Liquids in Synthesis (2nd ed), Wiley-VCH: Weinheim, Germany, 2007; 527-558; Scovazzo et al., J. Membr. Sci. 2004; 238: 57-63; and Jiang et al., J. Phys. Chem. B. 2007; 111: 5058-5061). RTILs can selectively permeate one gas over another (for example, CO2/CH4, CO2/N2, and SO2/CH4) or separate products from a reaction mixture such as during a transesterification reaction (Hernandez-Fernandez et al., J. Membr. Sci. 2007; 293: 73-80). Employment of supported ionic liquid membranes (SILMs) is attractive as RTILs possess negligible vapor pressures and can be impregnated into porous supports without evaporative losses, a hindrance for traditional supported liquid membranes (SLMs). However, regardless of the nature of the liquid in the support (RTILs or others) the SLM configuration can fail if the pressure differential across the membrane is great enough to overcome the liquid-support interactions and push the liquid through the pores of the support. While there are certainly a multitude of research applications where this pressure differential is not an issue, many industrial gas separations occur at much higher pressures than SLMs can withstand, typically only a few atmospheres (Baker, Ind. Eng. Chem. Res. 2002; 41: 1393-1411). In their current forms, SILMs are a more valuable tool for evaluating gas solubility, diffusivity, and separations in RTILs rather than a viable technology for industrial membrane separations (Ferguson et al., Ind. Eng. Chem. Res. 2007; 46: 1369-1374).
However, the idea of encapsulating RTILs in polymers and polymer membranes is not without merit. RTILs may be useful as non-volatile additives for improving polymer processing and properties (Winterton, J. Mater. Chem. 2006; 16: 4281-4293). RTILs could be better stabilized in polymer gas separation membranes if the support matrix is designed to provide enhanced interactions with RTILs. A number of different supports have been used in the study of SILMs for use as gas separation membranes, yet none of these polymers truly resembles the RTILs themselves (Ilconich et al., J. Membr. Sci. 2007; 298: 41-47). While the weak interactions between the RTILs and supports allow for gas diffusion as if it were a neat liquid, this configuration will inherently have limitations to the pressure differential that can be applied. Researchers in conductive polymers and liquid crystals (LCs) have given a good deal of consideration to composite structures where free RTILs are contained within the polymer or LC matrix (Ohno, Macromol. Symp. 2007; 249/250: 551-556; Nakajima et al., Polymer 2005; 46: 11499-11504; Yoshio et al., Mol. Cryst. Liq. Cryst. 2004; 413: 2235-2244; and Yoshio et al., J. Am. Chem. Soc. 2006; 128: 5570-5577).
Research in recent years of RTILs as selective gas separation media has focused primarily on CO2-based separations, with SO2 removal also appearing to be a promising pursuit (Jiang et al., Phys. Chem. B 2007, 111: 5058; Huang et al., Chem. Commun. 2006, 38:4027; and Anderson et al., J. Phys. Chem. B 2006, 110: 15059). RTILs, especially those based on imidazolium cations, exhibit an affinity for CO2 relative to CH4 and N2. CO2/CH4 separation is of critical importance to natural gas processing and improving fuel quality. CO2/N2 separation from flue gas streams (CO2 capture and sequestration) is an issue currently garnering significant global attention (Bara et al., Acc. Chem. Res. 2010, 43:152-159). RTILs have been proposed as alternative “green” solvents to replace the volatile organic compounds (VOCs) typically employed in CO2 scrubbing (Baltus et al., Sep. Sci. Technol. 2005, 40: 525; and Anthony et al., Int. J. Environ. Technol. Manage. 2005, 4: 105).
Several different approaches have been employed to exploit the desirable properties of RTILs for gas separation applications. Many experiments have focused on measuring the solubility of various gases of interest in RTILs at a range of pressures. The larger solubility of CO2 compared to CH4 and N2 could perhaps be utilized to achieve separation through pressure swing absorption. CO2 could be selectively absorbed into the RTIL solvent, while the less soluble gas is swept away, creating a CO2-lean stream. CO2 could then be desorbed from solution to produce a CO2-rich stream. This type of configuration appears more viable in RTILs than in traditional VOCs, as there is little risk of volatilizing RTILs in the desorption step. An inherent drawback of such a pressure swing configuration with RTILs is that the volume of solvent required is directly proportional to the volume of gas to be processed and inversely proportional to the concentration (partial pressure) of CO2 in the feed stream. As the largest solubility of CO2 in some common, imidazolium-based RTILs is ca. 0.08 mol L−1 atm−1 (2.2 cm3 (STP) cm−3 atm−1) at 40° C.; it becomes apparent that large volumes of RTILs would be required to process large volumes of low pressure CO2 from flue gas streams.
Supported ionic liquid membranes (SILMs) have been examined as a means to process CO2 in a selective RTIL medium without the need for large volumes of fluids (Scovazzo et al., J. Membr. Sci. 2004, 238: 57). SILMs can be prepared by “wetting” a porous polymer (or inorganic) support with an RTIL of interest. The volume of gas that can be processed is directly proportional to the membrane surface area and the feed pressure. Some SILMs exhibit ideal (i.e., single gas) CO2 permeability approaching 1000 barrers and ideal separation factors for CO2/N2 up to 60 or higher. When viewed on a “Robeson plot”, these data indicate that SILMs are highly competitive with polymer membranes and may be an industrially attractive technology for CO2/N2 separations. SILMs do not appear as viable in CO2/CH4 separations when examined on a “Robeson plot” for that separation (Camper et al., Ind. Eng. Chem. Res., 2006, 45: 6279; Robeson, L. M., J. Membr. Sci. 2008, 320: 390; and Robeson L. M., J. Membr. Sci. 1991, 62:165-185).
However, as a gas separation membrane platform, SILMs are not without their own drawbacks. In many supports, weak capillary forces hold the RTIL within the matrix. While the lack of strong RTIL-support interactions allows for high gas permeability through the liquid phase, this also negatively impacts the stability of the SILM configuration. The transmembrane pressure differentials that SILMs can withstand appear limited to a few atmospheres, before the RTIL is “squeezed” from the support. The long-term integrity of the support, especially those that are polymer-based, is also of concern.
There are several reports of imidazolium-based room temperature ionic liquids (RTILs) containing primary, secondary, and tertiary alcohol-functionalized cations (Holbrey et al., Green Chem. 2003, 5, 731-736; Camper et al., Ind. Eng. Chem. Res. 2008, 47, 8496-8498; Boesman et al., Monatschefte für Chemie 2007, 138, 1159-1161; and Arnold et al., C. Chem. Commun. 2005, 1743-1745). The primary alcohol functionality has been shown to influence the miscibility of imidazolium-based RTILs with 1° and 2° alkanolamines (Camper et al., Ind. Eng. Chem. Res. 2008, 47, 8496-8498). However, RTILs containing a vicinal diol on the cation are much less common, although they have been used as aldehyde protecting groups and ligands for Pd catalysis (Cai et al., Chin. Chem. Left. 2007, 18, 1205-1208; and Cai et al., Catal. Commun. 2008, 9, 1209-1213). The vicinal diol-functionalized RTILs used in these studies employed the PF6 anion, which has the liability of hydrolyzing and generating HF under certain conditions (Cai et al., Catal. Commun. 2008, 9, 1209-1213; and Visser et al., Ind. Eng. Chem. Res., 2000, 39, 3596-3960). Polymerizable imidazolium-based RTILs have been reported with bis(trifluoromethansulfonimide) anions and imidazolium-based cations containing a polymerizable styrene group and a n-alkyl chain, an oligo(ethylene glycol) linkage or a nitrile terminated n-alkyl chain (Bara et al., Polym. Adv. Technol., 2008, 19, 1415-1420; and Bara et al., Ind. Eng. Chem. Res., 2008, 47(24), 9919-9924).
RTIL polymers and materials of the present invention also show promise as antistatic agents and materials. An antistatic agent is a compound used for treatment of materials or their surfaces in order to reduce or eliminate buildup of static electricity. Its role is to make the surface or the material itself slightly conductive, either by being conductive itself, or by absorbing moisture from the air and relying on the conductivity of water for charge dissipation.
Electrostatic charge buildup is responsible for a variety of problems in the processing and use of many industrial products and materials (U.S. Pat. No. 6,592,988). Electrostatic charging can cause materials to stick together or to repel one another, which is particularly problematic in fiber and textile processing. In addition, static charge buildup can cause objects to attract unwanted particles such as dirt and dust. Among other things, this can decrease the effectiveness of fluorochemical repellents. Sudden electrostatic discharges from insulating objects can also be a serious problem. With photographic film, such discharges can cause fogging and the appearance of artifacts. When flammable materials are present, such as in high oxygen environments, a static electric discharge can serve as an ignition source, resulting in fires and/or explosions. Static buildup is a particular problem in the electronics industry, where electronic devices can be extremely susceptible to permanent damage by static electric discharges. Typical antistatic additives contain functional groups able to conduct electrical charges and include ethoxylated amines, fatty acids or esters, glycerol mono state, quaternary amines, and ionomers such as methacrylic acid/ethylene/NaI ionomers.
However, conventional antistatic materials have generally not been very effective in combination with fluorochemical repellents and often result in degradation of the antistatic characteristics, and undesirable erosion or interactions with the treated substrate material. For example, amines, ethoxylated amines and quaternary amines can be corrosive to polycarbonate substrates and metals on electronic components. Furthermore, it has been particularly difficult to combine conventional antistatic materials and fluorochemical repellents in polymer melt processing applications, as, for example, the water associated with humectant antistatic materials vaporizes rapidly at melt processing temperatures. This has resulted in the undesirable formation of bubbles in the polymer and has caused screw slippage in extrusion equipment. Many antistatic materials also lack the requisite thermal stability, leading to thermal degradation of the material. Thus, there remains a need in the art for antistatic agents that can be effectively combined to impart both good antistatic characteristics and are compatible to a wider range of substrates.